Evidence suggests limiting gun availability helps - from the article: As for the bomb example, bombs are difficult to make and often require testing, which means these people usually break the law before the attacks and police have a chance to find them. Columbine, for example, was primarily supposed to be a bombing, but most of the homemade bombs failed. It seems people who wanted to cause damage on that scale would use bombs regardless of gun laws, all evidence points to restricting gun access as helping.More than 60 percent of the attackers were not prohibited from possessing guns because of prior felonies or other reasons. But the organization still found there was less likelihood of mass killings in states that require background checks for all handgun sales than in states that do not — and even less chance of shootings by people who were prohibited by law from possessing firearms.